The present invention relates to a tube bender, and particularly to apparatus and methods for bending tubes of the type included in vehicle exhaust systems. More particularly, the present invention relates to a tube bender including a collet that is configured to grip a tube and also including a mandrel rod passing through the collet and into the tube.
A tube bender or tube-bending machine forms a tube into a desired shape by bending the tube at selected locations along the length of the tube in a tube-bending process. The first step in the tube-bending process is to mount an end of the tube on a collet included in the tube bender. Once mounted on the collet, the tube is moved relative to a die assembly also included in the tube bender. The die assembly engages the outer surface of the tube to form the tube so that it is moved to assume a desired bent shape.
Conventional tube benders include an external collet that grips the outer surface of the tube to be formed or bent in the tube bender. Because both the external collet and die assembly engage the outer surface of the tube, the external collet and die assembly must be spaced apart from one another to avoid interfering with one another. Because the external collet covers a portion of the tube and must be spaced apart from the die assembly, the end of the tube coupled to the external collet is prevented from being moved as close to the die assembly as desired when placing a bend in the end of the tube. This results in the end of the tube having an "unbendable portion" that typically is one to four inches (2.5 cm to 10.2 cm) in length. Such an unbendable portion (i.e. a portion that cannot be bent or otherwise formed in the die assembly) becomes a material-waste portion if a bend is required to be formed near the end of the tube. This material-waste portion of the tube must be removed by a cutting procedure. Thus, use of a conventional outer surface-gripping, external collet wastes material and increases manufacturing time and labor costs.
In a conventional tube-bending process known as "mandrel bending," a mandrel assembly is moved through a mandrel-receiving passageway formed in the external collet. The mandrel assembly includes a mandrel rod and a mandrel ball assembly coupled to the mandrel rod and positioned to lie within the tube adjacent to the die assembly to prevent the tube from "flattening out" during the tube-bending process. The mandrel ball assembly fills the tube at the location where the tube is being bent and thus prevents that portion of the tube at that location from being flattened.
According to the present invention, a tube-bending machine is provided for forming a tubular work piece having an inner surface. The tube-bending machine comprises a die assembly for forming the tubular work piece to assume a bent shape, an actuator system configured to move the tubular work piece to predetermined positions relative to the die assembly, a mandrel assembly including a mandrel rod having a first end and a second end spaced apart from the first end and a plurality of mandrel balls attached to the second end of the mandrel rod, and gripping means for gripping the inner surface of the tubular work piece during advancement of the tube towards the die assembly. The first end of the mandrel rod is attached to the actuator. The gripping means is coupled to the actuator system and formed to include a mandrel rod-receiving aperture. The mandrel rod is positioned to lie in the mandrel rod-receiving aperture.
In preferred embodiments of the present invention, the gripping means is an internal collet and an arbor assembly that allows the tube bender to move a tube towards the die assembly without interfering with the die assembly or other components of the tube bender. This allows a tube bender equipped with an internal collet configured to grip an inner surface of the tubular work piece to bend a portion of the tube not previously bendable by conventional outer surface-gripping, external collets. An internal collet in accordance with the present invention permits the end of the tube coupled to the internal collet to be placed closer to the die assembly than allowed by an external collet. This inner surface-gripping, internal collet reduces the amount of material waste and often eliminates the manufacturing step of cutting the material-waste portion off the tube. The present invention also allows for a mandrel assembly to be moved through a mandrel-receiving passageway formed in the internal collet to reduce the potential of the tube flattening during the tube-bending process.
A method in accordance with the present invention is provided for gripping a tube on a tube bender. The method includes the step of providing a tube having a collet-engaging end and an inner surface, a tube bender including a gripping assembly, and a mandrel assembly having a mandrel rod. The gripping assembly includes a collet having a plurality of tines and an arbor assembly having a mandrel rod-receiving aperture. The mandrel rod extends through the mandrel rod-receiving aperture. The collet-engaging end of the tube is placed over the plurality of tines of the collet. The arbor assembly moves relative to the collet so that the arbor assembly expands the plurality of tines to an expanded position so that the plurality of tines grip the inner surface of the tube. After the gripping assembly mounts the tube on the tube bender, the actuator system advances the tube to predetermined locations in relationship to the die assembly. The actuator system then advances the tube for each subsequent bend. After the tube has been advanced for the last bend and the die assembly has clamped the tube, the gripping assembly releases the tube and the actuator system removes the gripping assembly away from the die assembly.
In preferred embodiment of the present invention, the method of gripping a tube is provided where the tube end being gripped on its inner surface can be placed closer to the die assembly. By placing the tube end being gripped closer to the die assembly, bends can be placed in the end being gripped without leaving an unbendable waste portion that must later be removed. Thus, material is not wasted that must be cut off and disposed of at a later time. Furthermore, the method of the present invention provides a step for reducing or eliminating the potential for the tube to flatten out while being bent by the die assembly.
Additional features and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.